A transducing bacteriophage λ carrying the structural gene for elongation factor Ts

Summary A specialized transducing bacteriophage dpolCdapD-9 has been isolated that carries the structural gene for EF-Ts¹ (tsf). The presence of EF-Ts among the proteins synthesized under the direction of this phage in UVL-inactivated cells has been detected by two-dimensional gel electrophoresis and has been verified by antibody precipitation. In an induced lysogen of this phage the relative rate of synthesis of EF-Ts is increased 4-fold. Evidence is presented which suggests that the structural genes for ribosomal protein S2 (rpsB) and RNA polymerase factor (sit) also lies on dpolCdapD-9.     

Expression of a prokaryotic gene in yeast: isolation and characterization of mutants with increased expression

Summary The Escherichia coli Tn9 derived chloramphenicol resistance gene (cam ^r) is functionally expressed in the yeast Saccharomyces cerevisiae. This gene was introduced into yeast cells as part of a hybrid yeast/E. coli shuttle plasmid. A number of plasmid associated yeast mutants overproducing the cam ^r gene product, chloramphenicol acetyltransferase (acetyl-CoA: chloramphenicol 3-0-acetyltransferase, E.C. 2.3.1.28) were isolated. One of the plasmid mutants was analyzed in some detail. Even though this mutant showed a 1,000 fold overproduction of chloramphenicol acetyltransferase in the yeast host the level of RNA complementary to the cam ^r gene was not increased. A deletion of 127 base pairs in the region immediately upstream from the 5 end of the cam ^r gene appeared to be responsible for the up phenotype of this mutant. This mutation affected the expression of the cam ^r gene in E. coli in a down fashion, in contrast to its effect in yeast.     

Further evidence for abnormal protein kinase C regulation of macromolecule secretion in fibroblasts from cystic fibrosis patients

In comparison to skin fibroblasts from normal subjects, those from patients with cystic fibrosis (CF): (1) bound [20-³H] phorbol 12,13-dibutyrate (PDBu) with a higher affinity (K_d=25.8 vs 12.8 nM respectively) but expressed a similar number of total phorbol ester binding sites (about 2.5 pmol PDBu bound/mg of protein); (2) exhibited a faster and higher response to 4-phorbol 12-myristate 13-acetate (PMA) for the stimulation of [³⁵S]-labelled glycoconjutate release, but were equally sensitive to the synergistic effect of A23187 on this process; and (3) secreted glycoconjugates with similar [³⁵S]-sulfate and [¹⁴C]-leucine to [¹⁴C]-glucosamine labelling ratios. Taken together, these results provide further evidence for abnormal protein kinase C (PKC) regulation of macromolecule secretion in CF disease.Abbreviations BSA Bovine serum albumin - DBcAMP Dibutyryl cyclic AMP - DMEM Dulbecco's modified Eagle's medium - DMSO Dimethylsulfoxide - LDH Lactate dehydrogenase - PBS Phosphate-buffered saline - PDBu 4-phorbol 12,13-dibutyrate - 4-PDD 4-phorbol 12,13-didecanoate - PMA 4-phorbol 12-myristate 13-acetate - TCA Trichloroacetic acid     

Liquid-phase axial mixing in a bubble column bioreactor containing yeast suspensions

Summary Liquid-phase axial mixing coefficients were evaluated in a 0.15 m x 2.0 m batch bubble column containing water and yeast-in-water suspensions of different concentrations. Air superficial velocities ranged from 0 to 0.06 m/s. Axial mixing coefficients were calculated from the residence time distribution to an NaCl tracer pulse using the Ohki and Inuoe model. No specific variations in the calculated coefficients were observed to result from the presence of yeast cells. There was fair agreement between the data thus obtained and the only available data on mixing in non-Newtonian CMC solution.Nomenclature C _E equilibrium tracer concentration g/l - C tracer concentration at time t g/l - d_h sparger hole diameter m - D _t tube diameter m - D _z axial mixing coefficient m²/s - g acceleration of gravity m/s² - H _B bubbling layer heigh m - L longitudinal dustance between tracer injection and detection points m - n 1,2,6 Eq. (3) - t time s - U_g gas superficial velocity m/s - U_t liquid superficial velocity m/s - V _r bubble relative velocity = m/s - V _t Linear relative velocity m/s - z axial distance m Greek _c wet cell volume farction - _g gas holdup - _l liquid holdup - _l viscosity of the liquid phase Pa/s - _l density of liquid or continuous phase g/ml     

Production of 22:2<Superscript>Δ5,Δ13</Superscript> and 20:1<Superscript>Δ5</Superscript> in <Emphasis Type="Italic">Brassica carinata</Emphasis> and soybean breeding lines via introduction of <Emphasis Type="Italic">Limnanthes</Emphasis> genes

Seed oils of meadowfoam (Limnanthes douglasii, L. alba) contain very long-chain fatty acids of strategic importance for a number of industrial applications. These include the monoene 20 1⁵ and the diene 22:2^5,13. Engineering of meadowfoam-type oils in other oilseed crops is desirable for the production of these fatty acids as industrial feedstocks. Accordingly, we have targeted Brassica carinata and soybean (Glycine max) to trangenically engineer the biosynthesis of these unusual fatty acids. An L. douglasii seed-specific cDNA (designated Lim Des5) encoding a homolog of acyl-coenzyme A desaturases found in animals, fungi and cyanobacteria was expressed in B. carinata, which resulted in the accumulation of up to 10% 22:2^5,13 in the seed oil. In soybean, co-expression of Lim Des5 with a cDNA (Lim FAE1) encoding an FAEl (elongase complex condensing enzyme) homolog from L. douglasii resulted in the accumulation of 20:1⁵ to approximately 10% of the total fatty acids of seeds. The content of C₂₀ and C₂₂ fatty acids was also increased from <0.5% in non-transformed soybean seeds to >25% in seeds co-expressing the Lim. douglasii Des5 and FAE1 cDNAs. In contrast, expression of the Lim Des5 in Arabidopsis did not produce the expected 20:2^5,11 in the seed oil. Cumulatively, these results demonstrate the utility of soybean and B. carinata for the production of vegetable oils containing novel C₂₀ and C₂₂ fatty acids, and confirm that the preferred substrates of the Lim Des5 are 20:0 and 22:1³, respectively.     

The behaviour of yeast flocs in hindered settling and fluidized bed regimes

Summary Sedimentation and fluidization of yeast flocs were found to be non-synonymous processes. The analysis of Richardson and Zaki (1954) was found not to hold when applied to yeast flocs in both regimes. Partial support and channelling were implicated in the deviations from idela behaviour. Other factors responsible for the behaviour of yeast flocs in these regimes are discussed.Symbols D bed height (cm) - g gravitational constant (981 cm·s^-1) - n constant (-) - R retardation factor (s) - S constant (-) - v liquid/particle velocity (cm·s^-1) - V _o particle terminal velocity (cm·s^-1) - bed voidage (-)     

Hydrodynamic characteristics of two-phase inverse fluidized bed

Hydrodynamic characteristics of a new mode of liquid-solid fluidization, termed as inverse fluidization in which low density floating particles are fluidized with downward flow of liquid, are experimentally investigated. The experiments are carried out with low density particles (<534 kg/m³) which allow high liquid throughputs in the system. During the operation, three regimes, namely, packed, semi-fluidization and fully fluidization are encountered. Empirical correlations are proposed to predict the pressure drop in each regime. A computational procedure is developed to simulate the variation of pressure drop with liquid velocity.List of Symbols Ar modified Archimedes number, d _p ³ (– _s)g/² - d _p particle diameter, mm - f friction factor (eq. 2) - g acceleration due to gravity, m/s² - H total bed height, m - H _c height of the column, m - H_f height of fluidized bed, m - H₀ height of initial bed, m - H_p height of the packed bed, m - (p) pressure drop across the bed, N/m² - (p) _f pressure drop across fluidized bed section, N/m² - (p) _p pressure drop across the packed bed section, N/m² - (p) _sf total pressure drop in semifluidization regime, N/m² - Re Reynolds number, d _pU ₁/ - Re_m modified Reynolds number, d _pU ₁/(1– _p) - U ₁ superficial liquid velocity, m/s - U_mf minimum fluidization velocity, m/s - U_osf onset fluidization velocity, m/s Greek Letters _f voidage of fluidized bed - _p voidage of packed bed - liquid viscosity, kg/ms - liquid density, kg/m³ - _s particle density, kg/m³     

Performance,kinetics, and substrate utilization in a continuous yeast fermentation with cell recycle by ultrafiltration membranes

Summary A continuous single stage yeast fermentation with cell recycle by ultrafiltration membranes was operated at various recycle ratios. Cell concentration was increased 10.6 times, and ethanol concentration and fermentor productivity both 5.3 times with 97% recycle as compared to no recycle. Both specific growth rate and specific ethanol productivity followed the exponential ethanol inhibition form (specific productivity was constant up to 37.5 g/l of ethanol before decreasing), similar to that obtained without recycle, but with greater inhibition constants most likely due to toxins retained in the system at hight recycle ratios.By analyzing steady state data, the fractions of substrate used for cell growth, ethanol formation, and what which were wasted were accounted for. Yeast metabolism varied from mostly aerobic at low recycle ratios to mostly anaerobic at high recycle ratios at a constant dissolved oxygen concentration of 0.8 mg/kg. By increasing the cell recycle ratio, wasted substrate was reduced. When applied to ethanol fermentation, the familiar terminology of substrate used for Maintenance must be used with caution: it is not the same as the wasted substrate reported here.A general method for determining the best recycle ratio is presented; a balance among fermentor productivity, specific productivity, and wasted substrate needs to be made in recycle systems to approach an optimal design.Nomenclature B Bleed flow rate, l/h - C _T Concentration of toxins, arbitrary units - D Dilution rate, h^-1 - F Filtrate or permeate flow rate, removed from system, l/h - F _o Total feed flow rate to system, l/h - K _s Monod form constant, g/l - P Product (ethanol) concentration, g/l - P _o Ethanol concentration in feed, g/l - PP} Adjusted product concentration, g/l - PD Fermentor productivity, g/l-h - R Recycle ratio, F/F _o - S Substrate concentration in fermentor, g/l - S _o Substrate concentration in feed, g/l - V Working volume of fermentor, l - V _MB Viability based on methylene blue test - X Cell concentration, g dry cell/l - X _o Cell concentration in feed, g/l - Y _ATP Cellular yield from ATP, g cells/mol ATP - Y _ATPS Yield of ATP from substrate, mole ATP/mole glucose - Y _G True growth yield or maximum yield of cells from substrate, g cell/g glucose - Y _P Maximum theoretical yield of ethanol from glucose, 0.511 g ethanol/g glucose - Y _P/S Experimental yield of product from substrate, g ethanol/g glucose - Y _x/s Experimental yield of cells from substrate, g cell/g glucose - S _NP/X Non-product associated substrate utilization, g glucose/g cell - k ₁, k₂, k₃, k₄ Constants - k ₁ ^APP , k ₂ ^APP Apparent k ₁, k₃ - k ₁ ^TRUE True k ₁ - m Maintenance coefficient, g glucose/g cell-h - m ^* Coefficient of substrate not used for growth nor for ethanol formation, g glucose/g cell-h - Specific growth rate, g cells/g cells-h, reported as h^-1 - _m Maximum specific growth rate, h^-1 - v Specific productivity, g ethanol/g cell-h, reported as h^-1 - v _m Maximum specific productivity, h^-1     

Disintegration of yeast Saccharomyces cerevisiae in the vertical perl mill with a bell-shaped impeller

Investigation of disintegration of yeast Saccharomyces cerevisiae in the laboratory batch perl mill with a bell-shaped impeller was carried out. The number of non-damaged cells, changing in time was determined using hemocytometer (Thom's chamber).To describe kinetics of the disintegration process the differential equation was applied: where N _p the number of non-damaged cells in the sample, [number of cells/ml] t time, [s] m,k constants.The effect of three operating parameters: rotation frequency of the impeller shaft n, filling of the mill with disintegrating elements (ballotini) S _k and the initial concentration of yeast cells in the suspension C ₀ on the process of disintegration was analyzed.For S _k =0.5, m=1 and dependence of constant k on the rotation frequency of the impeller and suspension concentration were obtained. For S _k =0.6 and 0.7 the values of m were higher than 1. The effect of rotation frequency of the impeller and filling of the mill, with ballotini on constant k and exponent m was determined.List of Symbols a, b constants - a ₁, b ₁, c ₁, d ₁ constants - C ₀ initial concentration of suspension g/ml - C concentration of cell suspension g/ml - k constant disintegration rate 1/s; N ₀ ^1-m /s - m variable in the equation - N ₀ initial number of cells no. of cells/ml - N _p number of non-damaged cells no. of cells/ml - r process rate g/ml·s - X(t) disintegration degree % - , variables in the equation - z variable in the equation - S _k degree of filling the mill with disintegrating elements     

Protein entrainment during baker's yeast fermentation on a semi-solid substrate in an air-fluidized bed fermentor

Baker's yeast was grown on a semi-solid substrate (homogenized whole potatoes) in an air-fluidized bed fermentor, in which a rapid stream of air simultaneously supplied oxygen and mixed the semi-solid substrate. The potato starch was converted to reducing sugars by -amylase (from Aspergillus).During the course of the batch fermentation, some secreted yeast proteins were trapped by sparging the effluent air into a water chamber. Surprisingly, neither the -amylase nor the potato proteins were the most predominant proteins carried over to the overhead collector during the 24 h run, even though they were the most abundant proteins in the fermentation mash. Fractionation of the yeast-produced proteins during this carry-over process is described, based on gel electrophoresis analyses of both the carried-over proteins and the extracellular proteins in the fermentation bed. Effects of the operating variables on the extracellular protein levels in the fermentation bed and the proteins in the overhead collector are also discussed.     

High yeast concentration in continuous fermentation with cell recycle obtained by tangential microfiltration

Summary Continuous fermentation fed by 150 kg/m³ of glucose with total cell recycling by tangential microfiltration enabled yeasts concentration of 300 kg/m³ (dry weight) to be reached with a dilution rate of 0,5h^–1 and a cell viability greater than 75%. The stability of this system was tested for 50 residence times of the permeate. The method can be used both for the production of cell concentrates and for high rates of metabolite production.Nomenclature D. W. dry weight - X_T (kg/m³) total cell concentration D.W. - X_V (kg/m³) viable cell concentration D.W. - V viability of cell culture in per cent of total cell concentration - S (kg/m³) glucose concentration - P (kg/m³) ethanol concentration - D (h) dilution rate - R (kg/kg) fermentation yield - (h) specific growth rate - vp(kg/kg/h) specific alcohol production rate - (m) yeast size - (kg/kg) kg of intracellular water per kg of dry cells     

Absence of the glutamine-synthetase-linked methylammonium (ammonium)-transport system in the cyanobiont of Cycas-cyanobacterial symbiosis

Using the ammonium analogue ¹⁴CH₃NH ₃ ⁺ , ammonium transport was studied in the cyanobiont cells freshly isolated from the root nodules of Cycas revoluta. An L-methionine-dl-sulphoximine (MSX)-insensitive ammonium-transport system, which was dependent on membrane potential (), was found in the cyanobiont. However, the cyanobiont was incapable of metabolizing exogenous ¹⁴CH₃NH ₃ ⁺ or NH ₄ ⁺ because of the absence of another ammonium-transport system responsible for the uptake of ammonium for assimilation via glutamine synthetase (EC 6.3.1.2). Such a modification seems to be the result of symbiosis because the free-living cultured isolate, Anabaena cycadeae, has been shown to possess both the ammonium-transport systems.Abbreviations and symbol ATS/ATSs ammonium transport system/systems - Chl chlorophyll - GS glutamine synthetase - MSX L-methionine-dl-sulphoximine - membrane potential     

Unblocked statistical-coil tetrapeptides in aqueous solution: quantum-chemical computation of the carbon-13 NMR chemical shifts

We recently reported a theoretical characterization of representative ensembles of statistical-coil conformations for tetrapeptides with unblocked termini in aqueous solution, at pH 7. The results showed good agreement between the computed Boltzmann-averaged and experimentally-determined values for both the vicinal coupling constants ³J_NH and the -proton chemical shifts. Here, we carry out a cluster analysis of the ensembles of conformations generated in that study, and use them to compute the Boltzmann-averaged values of the quantum-chemical ¹³C chemical shifts for different amino acids in the unblocked tetrapeptides GGXA (where X stands for Phe, Arg, His, Glu, Ile, Lys, Gln, Tyr, Leu, Thr, Ala, Gly and Val). The values of the ¹³C chemical shifts in these thirteen amino acids (for which experimental data are available) were computed by using Density Functional Theory with a 6–311+G(2d,p) basis set. Good agreement is found in terms of both the correlation coefficient (R) and standard deviations of the difference between the computed Bolztmann-averaged and the NMR-determined values for the ¹³C chemical shifts. These results suggest that it may be possible to build a reliable theoretically-derived database of chemical shifts for statistical-coil residues. The results of the current study contribute to our understanding of the relations between chemical shifts, dihedral angles and vicinal coupling constants, ³J_NH. In addition, they can shed light as to how the statistical-coilconformation is related to the conformational preference of more structured states, such as the -helical conformation.     

A robust fed-batch feeding strategy for optimal parameter estimation for baker's yeast production

Parameter identification of structured models is often a problem in biotechnology, because the poor data situation and the number of unknown parameters only allow for inaccurate estimates. But often only a subset of all kinetic parameters of the model are of interest for production purposes, e.g. for fed-batch cultivation. These parameters should be estimated with a given accuracy. In addition, the experiments for information acquisition with respect to these parameters should be as simple as possible and should consider some practical restrictions. In this contribution a fed-batch feeding strategy is proposed to allow for an accurate estimation of yield and of critical growth rate of baker's yeast. The feeding also allows for economic and stereotyped use of staff and equipment and is therefore suitable for routine use in screening of strains and media. The overall pattern is similar to that one, usually used in production scale to minimize errors by limited model validity. After an initial phase for achieving a reproducible state three different growth rates are adjusted to cover the range of possible critical growth rates. From biomass and ethanol measurements yield and critical growth rate can be estimated with an accuracy of about 2.1%. The fermentation pattern ends up with a constant feeding rate to simulate a limited oxygen transfer rate and to allow for an uptake of residual sugar and ethanol before a dough test can be carried out. Beside experimental results simulations and sensitivity analyses are shown.List of Symbols P ethanol concentration - S substrate concentration - S _f substrate concentration in feed - T fermentation time - V fermenter volume - X biomass concentration - C measurement error covariance matrix - F Fisher information matrix - X state variables - Y output variables - X _p state sensitivity functions with respect to parameters - Y _p output sensitivity functions - e eigenvectors - k vector of limitation and inhibition parameters - n number of observations - q _in feeding stream - q _b stream for samples and ammonia feed - r vector of specific turnover rates - y vector of yields - specific weight - eigenvalues - specific growth rate - _set exponent in exponential feeding - standard deviation Dedicated to the 65th birthday of Professor Fritz Wagner.A. O. Ejiofor and B. O. Solomon are grateful to the Alexander von Humboldt Stiftung for granting them fellowships and to GBF for providing all the materials necessary for their successful research stay in Germany.     

A novel fungal ω3-desaturase with wide substrate specificity from arachidonic acid-producing Mortierella alpina 1S-4

A filamentous fungus, Mortierella alpina 1S-4, is capable of producing not only arachidonic acid (AA; 20:4n-6) but also eicosapentaenoic acid (EPA; 20:5n-3) below a cultural temperature of 20°C. Here, we describe the isolation and characterization of a gene (maw3) that encodes a novel 3-desaturase from M. alpina 1S-4. Based on the conserved sequence information for M. alpina 1S-4 12-desaturase and Saccharomyces kluyveri 3-desaturase, the 3-desaturase gene from M. alpina 1S-4 was cloned. Homology analysis of protein databases revealed that the amino acid sequence showed 51% identity, at the highest, with M. alpina 1S-4 12-desaturase, whereas it exhibited 36% identity with Sac. kluyveri 3-desaturase. The cloned cDNA was confirmed to encode the 3-desaturase by its expression in the yeast Sac. cerevisiae. Analysis of the fatty acid composition of the yeast transformant demonstrated that 18-carbon and 20-carbon n-3 polyunsaturated fatty acids (PUFAs) were accumulated through conversion of exogenous 18-carbon and 20-carbon n-6 PUFAs. The substrate specificity of the M. alpina 1S-4 3-desaturase differs from those of the known fungal 3-desaturases from Sac. kluyveri and Saprolegnia diclina. Plant, cyanobacterial and Sac. kluyveri 3-desaturases desaturate 18-carbon n-6 PUFAs, Spr. diclina 3-desaturase desaturates 20-carbon n-6 PUFAs and Caenorhabditis elegans 3-desaturase prefers 18-carbon n-6 PUFAs as substrates rather than 20-carbon n-6 PUFAs. The substrate specificity of M. alpina 1S-4 3-desaturase is rather similar to that of C. elegans 3-desaturase, but the M. alpina 3-desaturase can more effectively convert AA into EPA when expressed in yeast. The M. alpina 1S-4 3-desaturase is the first known fungal desaturase that uses both 18-carbon and 20-carbon n-6 PUFAs as substrates.     

Intraparticle mass-transfer resistance and apparent time stability of immobilized yeast alcohol dehydrogenase

The stability and, consequently, the lifetime of immobilized enzymes (IME) are important factors in practical applications of IME, especially so far as design and operation of the enzyme reactors are concerned. In this paper a model is presented which describes the effect of intraparticle diffusion on time stability behaviour of IME, and which has been verified experimentally by the two-substrate enzymic reaction. As a model reaction the ethanol oxidation catalysed by immobilized yeast alcohol dehydrogenase was chosen. The reaction was performed in the batch-recycle reactor at 303 K and pH-value 8.9, under the conditions of high ethanol concentration and low coenzyme (NAD⁺) concentration, so that NAD⁺ was the limiting substrate. The values of the apparent and intrinsic deactivation constant as well as the apparent relative lifetime of the enzyme were calculated.The results show that the diffusional resistance influences the time stability of the IME catalyst and that IME appears to be more stabilized under the larger diffusion resistance.List of Symbols C _A, C_B, C_E mol · m^–3 concentration of coenzyme NAD⁺, ethanol and enzyme, respectively - C _p mol · m³ concentration of reaction product NADH - d _p mm particle diameter - D _eff m² · s^–1 effective volume diffusivity of NAD⁺ within porous matrix - k _d s^–1 intrinsic deactivation constant - K _A, K_A, K_B mol · m^–3 kinetic constant defined by Eq. (1) - K _A ^x mol · m^–3 kinetic constant defined by Eq. (5) - r _A mol · m^–3 · s^–1 intrinsic reaction rate - R m particle radius - R _v mol · m^–3 · s^–1 observed reaction rate per unit volume of immobilized enzyme - t _E s enzyme deactivation time - t _r s reaction time - V mol · m^–3 · s^–1 maximum reaction rate in Eq. (1) - V ^x mol · m^–3 · s^–1 parameter defined by Eq. (4) - V _f m³ total volume of fluid in reactor - w _s kg mass of immobilized enzyme bed - factor defined by Eqs. (19) and (20) - kg · m^–3 density of immobilized enzyme bed - unstableness factor - effectiveness factor - Thiele modulus - relative half-lifetime of immobilized enzyme Index o values obtained with fresh immobilized enzyme     

Characterization of the physical properties of yeast flocs

Summary Physical characteristics, namely floc density function, floc size distribution, and relative floc strength, of a number of flocculent yeast types were measured. A straight-line relationship was found to exist between log values of size and density for the yeasts examined. Each yeast type had coefficients from this relationship which could be used to interpret settling behaviour. Indices of relative floc strength were also obtained and together with the floc density function allowed fuller interpretation of yeast settling than with simpler theories.Symbols a constant (g·cm^-3) - B ₂/B ₁ floc binding strength of floc₂ relative to floc₁ - d _f floc diameter (cm) - d _i image diameter on print (cm) - d _max maximum floc diameter (cm) - f _d Ploc effective density (g·cm^-3) - g gravitational constant (981 cm·s^-1) - K _p constant (-) - R _l rate of enlargement on film - R ₂ rate of enlargement on print - S _s density of suspending liquid phase (g·cm^-3) - S _f density of solid (floc) phase (g·cm^-3) - U _t terminal settling velocity (cm·s^-1) - u liquid viscosity (g·cm^-3·^-1)     

Performance characteristics of yeast growth in a modified airlift fermenter

Two types of airlift fermenters, conventional (UT-ALF) and modified (CDT-ALF) were investigated to evaluate their performance with respect to baker's yeast growth. The riser tube of conventional external loop airlift fermenter is replaced by a converging-diverging tube, which is named as modified airlift fermenter having downcomer to riser cross-sectional area ratio A _d /A _r =1.8.The results were compared for the two types of airlift fermenter. A modified growth kinetics model for baker's yeast with oxygen as limiting substrate, has been proposed. The values of K _s and K _d of the growth model were determined from experimental data. The proposed model represented better for CDT-ALF system compared to UT-ALF. Compared to UT-ALF, CDT-ALF always showed higher cell mass concentration and low residual sugar concentration irrespective of the operating conditions. At optimum operating condition (initial glucose concentration 30 g/l, air flow rate 0.5 vvm and fermentation time 8 hrs.) 16.7% higher cell mass was observed in CDT-ALF compared to that in UT-ALF and yield (Y _x/s ) was found to be 0.51 which was theoretically very near to maximum achievable value.Symbols ALF Airlift fermenter - UT Uniform tube - CDT Converging-diverging tube - A _r Cross sectional area of riser - A _d Cross sectional area of downcomer - C _s Glucose cone, at any time, g/l - C _l Dissolved oxygen conc, at any time, g/l - _max Max. sp. growth rate, hr^–1 - Sp. growth rate, hr^–1 - X ₀ Initial cell mass cone. (dry wt.), g/l - X Cell mass conc. at any time t, g/l - C _s0 Initial glucose conc., g/l - C _s Glucose conc. at any time t, g/l - C _l Equilibrium conc. of oxygen, 0.0076 g/l - y _x/s Yield coefficient (dimensionless) - y _x/s gm cell mass produced/gm glucose consumed - Y _O2 gm cell produced/gm oxygen consumed - k _d maintenance coefficient, hr^–1 - K _L a volumetric mass transfer coefficient, hr^–1 - k _s saturation constant for the substrate, g/l - K _O2 saturation constant for the substrate of dissolved oxygen, g/l. This work was supported by a research grant from the Department of Biotechnology Govt. of India.     

Effects of beta-amyloid on proliferation and morphology of yeast Saccharomyces cerevisiae

Deposition of beta-amyloid peptide (1–42) (AP) in the brain is an early event linked with pathogenesis of cell injury and death in Alzheimer disease. Previous studies have demonstrated that AP induces cytotoxicity in several types of human cells. Surprisingly, the peptide was found not only to be non toxic for yeast cells, but to stimulate growth of yeast culture. The results are consistent with AP binding to yeast cell as illustrated by binding isotherms with theapparent dissociation constant of 8 × 10^-7 M and B_max of 4.7 × 10⁴ molecules/cell.     

Oxygen mass transfer in a bubble column bioreactor containing lysed yeast suspensions

Summary Liquid-phase volumetric oxygen transfer coefficients were evaluated in a bubble column containing yeast suspensions, using the instationary oxygen absorption method and a polarographic oxygen electrode. The electrode time lag was found to be independent of both the system studied and the operating conditions. The volumetric oxygen mass transfer coefficients k _L a could be reasonably predicted by calculating k _L from the equation derived by Bhavaraju et al. or the empirical equation of Calderbank and Moo-Young and a from the experimental gas hold-up values.Nomenclature a Exponent in Eq.6 or specific gas-liquid interfacial area based on reactor volume m - b Exponent in Eq. 6 - C Constant in Eq 6 or oxygen concentration in the liquid phase g/ml - C ^* Equilibrium oxygen concentration g/ml - C ₀ Oxygen concentration in the liquid phase at t=0 g/ml - C _E Oxygen concentration as determined by the polarographic electrode g/ml - D _B Bubble equivalent diameter mm - D _l Oxygen diffusivity in the liquid phase m²/s - g Acceleration of gravity m/s² - K Consistency index Pasⁿ - K _L Liquid-phase mass transfer coefficient m/s - n Power law exponent - Pe _sw Peclet number based on bubble swarm velocity - S _C Schmidt number - Sh Sherwood number - i Time s - U _B Bubble rise velocity in infinite medium m/s - U _g Superficial air velocity based on column cross-sectional area m/s - U _sw Bubble swarm velocity defined by Eq.15 m/s - Y _MSW Mass transfer coeficient correction factor for mobile interfaces in pseudo-plastic fluids Eq. 7 - Y _MSW Mass transfer coefficient correction factor for immobile interface in pseudo-plastic fluids Eq. 8 Greek letters _l Density of liquid g/ml - _sus Density of unaerated suspension g/ml - _{wet cell} Density of yeast wet cells g/ml - _l Viscosity of the liquid Pas - _app Apparent viscosity of power law fluid Pas - _E Electrode time lag s - _l Time lag due to resistance of the gas-liquid interface s - _g Gas hold-up, volume fraction occupied by the gas phase - _l Liquid hold-up - _c Wet cell volume fraction